Generally, a packaging bag in which contents such as snack foods are packaged is subjected to a seal check in order to detect bags whose contents may quickly deteriorate due to a faulty seal. Devices that conduct such a seal check are, for example, the seal checkers disclosed in Japanese Patent Application Publication No. 2002-211521 and Japanese Patent Application Publication No. 2003-156403.
With the seal checkers disclosed in the above mentioned publications, in the course of conveying a packaging bag supplied from the upstream side of the seal checker while sandwiching the packaging bag between upper and lower transfer conveyors, the seal checker will press the packaging bag by using the upper transfer conveyor, and detect the displacement of the upper transfer conveyor or the reaction force to the pressure which acts on the upper transfer conveyor at the time of pressing, and thereby conduct the seal check of the packaging bag.
As an example, the seal checker described in Japanese Patent Application Publication No. 2002-211521 will be described. As shown in FIG. 12, this seal checker 100 includes lower and upper transfer conveyors 110, 120. First, the lower transfer conveyor 110 is supported by a mounting frame 100A and a double column support 100B, and includes rollers 111A, 111B disposed at both end portions and a conveyor belt 112 wound between the rollers 111A, 111B. On the other hand, the upper transfer conveyor 120 is supported by a pair of support plates 100C, 100C fixed to the upper portions of the double column support 100B extending upward from the mounting frame 100A. The upper transfer conveyor 120 includes seven rollers 121A to 121G and a conveyor belt 123 wound between these rollers 121A to 121G. The seven rollers 121A to 121G are arranged at illustrated positions between the support plates 100C, 100C and between a pair of frame members 122, 122 (only the one in front is shown) on the lower side.
In addition, a motor 131 is mounted to the lower portion of the double column support 100B. The power of this motor 131 is transmitted to the roller 111A of the lower transfer conveyor 110 via a first timing belt 132A wound as illustrated in the figure, and then transmitted to the roller 121F of the upper transfer conveyor 120 via the first timing belt 132A and second and third timing belts 132B, 132C wound as illustrated in the figure. As a result, the lower and upper conveyor belts 112, 123 will run so as to convey a packaging bag X in the arrow E7 direction.
In addition, an upper end portion of a first link member 141A inclined and extending upwardly to the upstream side from the roller 121B is coupled to the roller 121C. On the other hand, an upper end portion of a second link member 141B inclined and extending upwardly to the upstream side from the roller 121A is coupled to the roller 121G. In other words, the support plate 100C on the upper side, the frame member 122 on the lower side, and the first and second link members 141A, 141B together constitute a four-node parallel linkage mechanism L1 that moves in the direction as shown by the arrows with the support plate 100C serving as the supporting point.
In addition, a servo motor 151 is mounted to the support plate 100C on the upper side. The output shaft of the servo motor 151 is connected to the vicinity of a lower end portion of a link member 141A on the upstream side via a lever member 152A and an intermediate link member 152B. Accordingly, the supplied packaging bag X comes in contact with and pushes up the upper transfer conveyor 120, and subsequently is sandwiched and pressed between the transfer conveyors 110, 120. Then, the distance between the transfer conveyors 110, 120 when the packaging bag is pressed thereby is detected by the servo motor 151 via the movement of the parallel linkage mechanism L1, and the seal check of the packaging bag X is conducted based on the detection result.